1. Field of the Invention
The present invention relates to a light source apparatus and a control method thereof.
2. Description of the Related Art
A light source apparatus comprising a plurality of light emission areas individually capable of controlling the emission brightness thereof has been known as a backlight of a liquid crystal display apparatus. There is also a technology for controlling the emission brightness of each light emission area in accordance with the degree of luminous intensity (level of brightness) of an input image signal. Such control is called “local dimming control.” One of the light emission area has three types of light emitting diodes (LEDs) as light sources, such as a red LED, a green LED, and a blue LED.
Also, Japanese Patent Application Publication No. 2008-40073 and WO 2003/077013, for example, disclose conventional technologies for improving the color reproducibility of a display apparatus having an independent light source.
Japanese Patent Application Publication No. 2008-40073 discloses a technology pertaining to a projector that has a plurality of light sources generating different emission colors and a plurality of liquid crystal light bulbs corresponding to the plurality of light sources. The plurality of light bulbs modulate (transmit) light of the light sources, and the resultant transmittances are controlled in response to image signals. The technology disclosed in Japanese Patent Application Publication No. 2008-40073 controls the emission brightness of each of the plurality of light sources in response to an input image signal and then corrects a gradation value of the input image signal in such a manner that the relationship between the gradation value of the input image signal and the brightness (relatively value) of the projector becomes equivalent among the light sources.
WO 2003/077013 discloses a technology for calculating an intensity distribution of the light from a light source by means of a known method (e.g., a method using a function describing how the light of the light source diffuses) and correcting an image signal based on the calculated intensity distribution.
Incidentally, the light from light emission areas diffuses, reflects and gets mixed inside a light source apparatus. For this reason, the colors of the light emission areas are determined by the mixed light. When the wavelength (emission wavelength) and the brightness (emission brightness) of the light generated by each light emission area are equal to each other, the color of the mixed light becomes even among the light emission areas. However, due to individual differences between light emitting elements such as LEDs, dispersion on manufacture and the like cause the variation in emission wavelengths, even -when the LEDs of the same type are used (LEDs emitting the same color). Such variation in emission wavelengths causes color unevenness (variation in the mixed light) in the light emission areas. Moreover, this color unevenness fluctuates depending on the emission brightness of the light emission areas.
Changes in colors of the light emission areas caused by changes in emission brightness thereof are described with reference to FIGS. 9A and 9B.
FIGS. 9A and 9B are diagrams schematically showing how the colors of three light emission areas change, the light emission areas being arranged in one direction.
FIG. 9A shows an example in which all of the light emission areas are caused to emit light at the same emission brightness (sufficiently high emission brightness; first emission brightness). Light emission areas 901, 902, 903 each have three LEDs as light sources: a red LED, a green LED, and a blue LED.
A brightness distribution 921a indicates a brightness distribution (simple brightness distribution) obtained when only the light emission area 901 is caused to emit light at the first emission brightness. A brightness distribution 922a indicates a brightness distribution obtained when only the light emission area 902 is caused to emit light at the first emission brightness. A brightness distribution 923a indicates a brightness distribution obtained when only the light emission area 903 is caused to emit light at the first emission brightness.
A brightness distribution 920a indicates a brightness distribution (synthetic brightness distribution) obtained when the light emission areas 901, 902, 903 are caused to emit light at the first emission brightness. In other words, the brightness distribution 920a is obtained by synthesizing the brightness distributions 921a, 922a, 923a. Because the light emission areas 901, 902, 903 have the same emission brightness, the brightness distribution 920a has a flat brightness distribution.
An emission wavelength 911a indicates a spectrum (simple spectrum) of the light emitted only by the light emission area 901 at the first emission brightness. An emission wavelength 912a indicates a spectrum of the light emitted only by the light emission area 902 at the first emission brightness. An emission wavelength 913a indicates a spectrum of the light emitted only by the light emission area 903 at the first emission brightness. In the emission wavelength 912a, the reference position shown by a dashed line exactly overlaps with the center of the entire emission wavelength interval. The emission wavelength 911a is a spectrum obtained by shifting the emission wavelength 912a towards the shorter wavelengths. The emission wavelength 913a is a spectrum obtained by shifting the emission wavelength 912a towards the longer wavelengths. Such spectra change randomly, which occurs due to individual differences between the LEDs.
A wavelength 931a indicates the color of the light emission area 901 obtained when the light emission areas 901, 902 and 903 are caused to emit light at the first emission brightness. Specifically, the wavelength 931a indicates a spectrum (synthetic spectrum) of the synthetic light (mixed light) generated in the light emission area 901 when the light, emission areas 901, 902 and 903 are caused to emit light at the first emission brightness. A wavelength 932a indicates a spectrum of synthetic light generated in the light emission area 902 when the light emission areas 901, 902 and 903 are caused to emit light at the first emission brightness. A wavelength 933a indicates a spectrum of synthetic light generated in the light emission area 903 when the light emission areas 901, 902 and 903 are caused to emit light at the first emission brightness. The wavelengths 931a, 932a and 933a are spectra that are substantially equal to one another due to the influence of light from other light emission areas. Thus, such color unevenness described above does not occur in these areas.
FIG. 9B shows an example in which the emission brightness of the light emission areas 901 and 903 is set at the first emission brightness and the emission brightness of the light emission area 902 is set at second emission brightness lower than the first emission brightness.
A brightness distribution 921b is obtained when only the light emission area 901 is caused to emit light at the first emission brightness. A brightness distribution 922b is obtained when only the light emission area 902 is caused to emit light at the second emission brightness. A brightness distribution 923b is obtained when only the light emission area 903 is caused to emit light at the first emission brightness.
A brightness distribution 920b is obtained when the light emission areas 901 and 903 are caused to emit light at the first emission brightness and the light emission area 902 is caused to emit light at the second emission brightness. In other words, the brightness distribution 920b is obtained by synthesizing the brightness distributions 921b, 922b and 923b. Because the emission brightness of the light emission area 902 is lower than those of the light emission areas 901 and 903, the brightness distribution 920b has the brightness decreasing on the light emission area 902.
An emission wavelength 911b indicates a spectrum of light emitted only by the light emission area 901 at the first emission brightness. An emission wavelength 912b indicates a spectrum of light emitted only by the light emission area 902 at the second emission brightness. An emission wavelength 913b indicates a spectrum of light emitted only by the light emission area 903 at the first emission brightness. As with FIG. 9A, in the emission wavelength 912b, the reference position shown by a dashed line exactly overlaps with the center of the entire emission wavelength interval. The emission wavelength 911b is a spectrum obtained by shifting the emission wavelength 912b towards the shorter wavelengths. The emission wavelength 913b is a spectrum obtained by shifting the emission wavelength 912b towards the longer wavelengths.
A wavelength 931b indicates a spectrum of the synthetic light generated in the light emission area 901 when the light emission areas 901 and 903 are caused to emit light at the first emission brightness and the light emission area 902 is caused to emit light at the second emission brightness. A wavelength 932b indicates a spectrum of synthetic light generated in the light emission area 902 when the light emission areas 901 and 903 are caused to emit light at the first emission brightness and the light emission area 902 is caused to emit light at the second emission brightness. A wavelength 933b indicates a spectrum of synthetic light generated in the light emission area 903 when the light emission areas 901 and 903 are caused to emit light at the first emission brightness and the light emission area 902 is caused to emit light at the second emission brightness. Because the emission brightness of the light emission area 902 is low, the light of the light emission area 902 does not so much leak to the other light emission areas. Therefore, the spectra of the wavelengths 931a, 932a and 933a are different from one another, causing the color unevenness described above. Due to such a color change, the colors of the image displayed by the display apparatus fluctuate, lowering its color reproducibility.
Unfortunately, these conventional technologies do not take such color unevenness (changes in colors of light emitted by the other light emission areas) into consideration. Thus, the use of such conventional technologies cannot contribute to suppression of changes in colors of the light emission areas or reduction of color reproducibility.